The CVT has widely been employed in a vehicle driving system. The CVT incorporates a metal belt that includes a metal member called an element. Prior art techniques related to the element are disclosed in Patent Documents 1 and 2.
The technique disclosed in Patent Document 1 will be described with reference to FIG. 17 hereof.
FIG. 17 is a diagram for explaining a conventional method of manufacturing an element for a CVT belt, in which a coiled material 100 is fed as indicated by an arrow 101, during which a large U-shaped relief opening 102 is first punched and then a plurality of recesses 103, 104, and 105 are formed. Finally, an element 110 is cut out from the coiled material 100, the element 110 including a body portion 107, a neck portion 108 extending from the body portion 107, and a head portion 109 disposed at the tip of the neck portion 108.
This is advantageous in the mass-productivity of the element 110 due to the continuous manufacture of the element 110 from the coiled material 100.
However, the ratio of the area of the element 110 to the area of the coiled material 100 is small, resulting in a poor yield.
A measure to improve the yield is proposed in Patent Document 2.
A technique disposed in Patent Document 2 will be described with reference to FIG. 18.
FIG. 18 is a diagram for explaining another conventional method of manufacturing an element for a CVT belt.
As depicted in (a) of FIG. 18, an element 120 includes a body portion 121, a neck portion 122 extending upwardly from the body portion 121, and a head portion 123 disposed on top of the neck portion 122.
As depicted in (b) of FIG. 18 that is a cross-sectional view taken along line b-b of (a), the body portion 121 is provided with a downwardly projecting taper portion 124, and the head portion 123 is provided with a raised portion called a nose 125 and a recessed portion called a hole 126.
The element 120 having such a shape is manufactured through (c) and (d) of FIG. 18.
That is, as depicted in (c), the taper portions 124, 124 are formed on the underside of a strip stock 127. This forming is carried out by causing the strip stock 127 to pass through between specialized reduction rolls.
Next, as depicted in (d), the nose 125 and the hole 126 are formed, and finally, left and right, two elements 120, 120 are obtained by blanking.
The yield is improved since the left and right, two elements 120, 120 can be obtained. However, the production cost increases due to the necessity of a specialized rolling machine to form the taper portions 124, 124. That is, the presence of a separate taper portion forming step induces an increase of the production cost.
An element manufacturing method is thus required in which the taper portion forming step depicted in (c) can be omitted.